This invention concerns a device for the crossed displacement of rolling rolls, whether they be working rolls and/or back-up rolls.
To be more exact, the invention is applied in cooperation with the upper and lower rolling blocks of a four-high rolling mill stand for plate and/or strip in order to permit a crossed and coordinated displacement of the working rolls and/or back-up rolls.
The state of the art covers four-high rolling mill stands for plate and/or strip which include opposed upper and lower working rolls which define the rolling plane and are fitted to the relative chocks located on one side and the other of the rolling mill stand.
Each working roll is associated with a relative back-up roll, the function of which is to limit the bends produced in the working roll during rolling, thus allowing very high rolling pressures to be used.
The state of the art covers the need to induce in the rolls a displacement in the rolling plane which causes a reciprocal crossed positioning of the rolls even though at very limited angles.
In the state of the art, this crossing movement is generally carried out by using two different techniques.
According to a first technique, traversing movements are imparted in a suitable direction to all the chocks supporting the rolls.
In order to achieve the crossed positioning of the rolls, each chock positioned at one end of a roll, for example a working roll, receives a traversing movement in the opposite direction to the movement imparted to the opposite chock of the same working roll and to the movement imparted to the chock at the same end of the opposed working roll.
By using this technique, the vertical projection of the point of intersection of the axes of the rolls remains unchanged for any angle imparted to the axes of the rolls.
According to another displacement technique, by displacing only the opposed chocks located on one side of the roll, while the chocks located on the opposite side are kept stationary, the position of the vertical projection of the point of crossover of the axes of the rolls is varied.
In the state of the art, a plurality of systems to displace the chocks have been proposed, for example with gear systems, screw-threaded systems, jack systems and others.
All these systems however have been found unsatisfactory with regard to accuracy of positioning, coordination of the movements, simplicity of embodiment and application, installation costs and other reasons, among which are the considerable power required, the considerable bending caused, the incorrect functioning of the bearings, etc.
Moreover, these systems known to the state of the art involve very long and laborious inspection and/or maintenance times, both because of their complex embodiments and also because of their positioning, as access is only possible with difficulty, or the maintenance/repair workers can only reach them after preliminary operations of at least partial dismantling of the rolling mill stand, carried out when the plant has been stopped, with all the technical and economic problems which that causes.
U.S. Pat. No. 1,971,982 provides to obtain the lateral movement and positioning of the chock with a pair of male-female threaded connections.
The connections have the disadvantage that they require a considerable specific pressure, a high number of revolutions to be imparted to one or the other of the components in order to obtain the desired displacement, a considerable precision of connection and a considerable axial length.
U.S. Pat. No. 3,197,986 of 1961 provides for front cam systems to adjust the working pressure and therefore the space between the working rolls. It is a dynamic adjustment system associated with the thickness of the rolled strip and to the maintenance of the desired value of thickness.